1. Three Types of Experiments
Completely Randomized
Block
Matched Pairs

2. Designing an Experiment
Block Design--divide subjects into groups (called blocks). All subjects in a block should be similar.
Randomly assign each treatment to one or more subjects in each block.
Block if you have reason to believe certain groups will have different results.
Matched-Pair Design--assigned either two matched individuals (identical twins) OR the same individual to receive the different treatments (Randomize the order of treatment)
Matched-Pair design is a special case of a Block design.

3. Randomized Block Design
7--Heavy
Measure & compare between groups
7--Moderate
21-- Children aged 5-10
Randomly assigned to 3 groups
7--Control
7--Heavy
43 volunteers blocked by age
Measure & compare between groups
(MOS, p.61-62) Researchers at the Univ. of Mass. Conducted a randomized experiment on 43 volunteers between 5.2 and 11.8 years of age. Children were recruited from a YNCA after school program.
The explanatory variable was carrying out the weight-lifting treatments and comparing muscular strength and endurance (response variable). Exercises were twice a week for 8 weeks. Higher repetitions with moderate rate showed the best results (40.9%) over the low-repetitions-heavy load at 31% increase.
22-- Children aged 11-16
Randomly assigned to 3 groups
8--Moderate
7--Control
Block by age because we believe younger children might have different results than older children

4. Randomly assigned to 2 groups
Matched Pair Design
Measure increases in strength & endurance & compare between groups
21—Heavy load for six weeks, rest two weeks, moderate load for six weeks
43 volunteers
Randomly assigned to 2 groups
(MOS, p.61-62) Researchers at the Univ. of Mass. Conducted a randomized experiment on 43 volunteers between 5.2 and 11.8 years of age. Children were recruited from a YNCA after school program.
The explanatory variable was carrying out the weight-lifting treatments and comparing muscular strength and endurance (response variable). Exercises were twice a week for 8 weeks. Higher repetitions with moderate rate showed the best results (40.9%) over the low-repetitions-heavy load at 31% increase.
22 – Moderate load for six weeks, rest two weeks, heavy load for six weeks

5. Which type of experiment?
Is the right hand of right-handed people generally stronger that the left? Paul Murky of Murky Research designs an experiment to test this question. He fastens an ordinary bathroom scale to a shelf five feet from the floor, with the end of the scale projecting out from the shelf. Subjects squeeze the scale between their thumb and their fingers on the top. A scale, which reads in pounds, will be used to measure hand strength.

6. Matched Pairs Design
Randomly assign ½ of the people to test right and then left hand, and the other ½ to test left hand first, and then right hand.
Make sure the participants cannot read the scale so they don’t influence themselves into trying to “top their score”.
Compare the differences in hand strength.

7. Which type of experiment?
An agronomist wishes to compare the yield of five corn varieties. The field, in which the experiment will be carried out, increases in fertility from north to south.

8. Block design
Block the field on location since fertility increases from north to south. (each color is one block)
Randomly assign each plot within the block to 1 of the 5 corn varieties (1-5).
Compare the yield of corn from each of the plots of land.